Energy converter



p 7, 1965 H. HUBER ETAL 3,205,380

ENERGY CONVERTER Filed May 5. 1961 2 Sheets-Sheet 1 INVENTORS H-HUBER et J-BENSIMON BY M ATTO RN EYS H. HUBER ETAL Sept. 7, 1965 ENERGY CONVERTER 2 Sheets-Sheet 2 Filed May 5, 1961 FIG.5

INVENTORS mwaen a J-BENSIMON ATTORNEYS United States Patent 4 Claims. icl. 310-4 The present invention relates to direct thermo-electronic converters for converting directly thermal energy into electrical energy.

It is known that, in its simplest form, such a converter comprises a pair of electrodes, particularly an emitter and a collector of electrons, disposed within a vacuumtight enclosure at a reciprocal distance, preferably not greater than the average free path of electrons within the medium filling the enclosure. These electrodes may be insulated between themselves or may be connected with each other by a relatively resistant metallic conductor, however, in any case, no voltage from an external source is applied therebetween. When heat is applied to the emitter, the energy of certain electrons within the emissive material increases beyond the working potential, whereupon these electrons leave the emitter and move in the direction toward the collector, provided that the effects of inter-electrode space charge are not too significant. If the working potential of the material of the collector is less than that of the emitter, the portion of the energy of the electrons captured by the collector which corresponds to the working potential thereof is dissipated in the form of heat, whereas the remaining portion which corresponds to the difference of the working potentials of the .two electrodes represents the difference of the contact potential and appears between the emitter and the collector in the form of an electric voltage which may be applied to a charging resistance suitably matched thereto.

As has already been indicated, the possibility of operation of such prior art device depends on the absence or the negligible significance of the space-charge effects. It is, therefore, necessary to compensate for the latter, and it is also also known to do so by introducing into the enclosure an ionizable gas or vapor of which the ionization potential is less than the working potential of the material of the surface of a conductor on which fall the atoms of the gas or of the vapor of the medium filling the enclosure which condense thereon. This surface may be that of the emitter or that of a separate supplementary electrode in which case the converter is no longer a diode but becomes a triode. If this surface is sufiiciently hot in order that the atoms can re-evaporate, many among them lose an electron and escape from the surface in the form of positive ions. By this phenomena, known under the name of surface or contact ionization, there are ob- ,tained ions which intermingle or mix with the electrons of the space charge and neutralize the charge thereof by forming a plasma. The converters utilizing this manner of compensating the space charge are commonly known as plasma converters or wet converters, and the present invention relates in particular to this type of converter.

The theory indicates that there exists an interest to cause the emitter to function at a temperature as elevated as possible, which also increases the emission current, and to cause the collector to operate at a temeprature sufficiently low in order that the electron emission thereof is negligible. Nevertheless, insofar as the temperature of the emitter is concerned, one approaches rapidly the limit with the known converters, for the speed of exaporation of the emissive material is an exponential function of the temperature, and if the latter is too high, the emissive material is deposited on the collector and, having itself a working potential higher than that of the collector, increases the working potential of the latter by increasing the losses to the detriment of the useful voltage. Additionally, the interelectrode space which is very small since the free path of the electrons in the plasma, for example, of cesium, is of the order of a fraction of a millimeter, risks to become short-circuited by the depositions of emissive material.

The object of the present invention is a Wet thermoelectronic converter for converting thermal energy directly into electrical energy, in which the emitter may function at a high temperature without the danger that the depositions of the emissive material form themselves at the surface of the collector or short-circuit the interelectrode space.

Accordingly, it is an object of the present invention to provide a thermo-electronic converter, especially of the wet type in which the collector electrode is made of a metal that is liquid at the normal operating temperatures of the converter.

Another object of the present invention resides in the provision of collector electrode structure in which the danger of impairment to the proper operation of the device as a result of deposits of emissive material from the emitter on the collector are effectively eliminated.

A further object of the present invention resides in the provision of a therrno-electronic converter of the type mentioned hereinabove which permits operation of the converter in a number of positions diiferent from that normally imposed by acceleration or gravitational forces.

Still another object of the present invention resides in the provision of a thermo-electronic converter adapted to convert directly thermal energy into electrical energy in which the collector material is so chosen as to be readily ionizable, provide sufficient vapor tension even at the relatively low pressures prevailing within the evacuated enclosure, produces essentially no electron emission at the operation temperature and has a low melting point as well as a specific weight lower than the emissive material from the emitter electrode to improve the operating characteristics of the device.

A further object of the present invention resides in the provision of a collector electrode structure for a thermo-electronic energy converter which permits the effective removal of deposits that would ordinarily collect on the surface of the collector electrode.

A still further object of the present invention resides in the provision of a thermo-electronic converter of the type mentioned hereinabove which produces a more homogenious plasma to effectively compensate for the space charge elfects.

These and other objects, features and advantages of the present invention will becomes more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of ilv3) ustration only, several embodiments in accordance with the present invention, and wherein:

FIGURE 1 is a cross sectional view through a first embodiment of a diode converter with a liquid collector in accordance with the present invention;

FIGURE 2 is a cross sectional view, similar to FIG- URE 1, of a modified embodiment of a converter in accordance with the present invention, and

FIGURE 3 is a cross sectional view of still another modified embodiment of a thermo-electronic converter in accordance with the present invention provided with means to evacuate the deposits of evaporated material.

According to the present invention, there is utilized as collector a metal which presents, in addition to the required qualities from the general point of view for the proper operation of the converter such as low working potential relative to the working potential of the material of the emitter, practical absence of electron emission at the temperatures of operation, etc., the following physical characteristics:

Low fusion point in such a manner as to remain in the liquid state at the operating temperature, itself as low as possible;

Relatively high boiling point, substantially higher than the temperature of intended operation, also taking into consideration the low pressure within the enclosure; and

A specific Weight lower than that of the materials which may be evaporated by the emitter.

The advantages of such a collector, which correspond to the suppression of the shortcomings mentioned hereinabove, result directly from the fact that the materials evaporated by the emitter do not remain on the surface of the collector but will fall to the bottom of the tank containing the liquid metallic mass at the temperature of operation.

Furthermore, measures may be taken also to evacuate the impurities which accumulate in the tank.

According to a further characteristic of the present invention, the metal chosen as collector may also be one of those which are utilizable as ionizable vapor source with a view to compensate the space charge. Since the ionizable vapor is then discharged from a large surface facing the emitter, there is obtained also the advantage of having a more homogeneous plasma than in the case in which this vapor is derived from a source situated outside of these two relatively large surfaces facing each other.

In addition to the characteristics enumerated hereinabove, this metal must also have the following supplementary characteristics:

It must be readily ionizable, that is, have an ionization potential lower than the working potential of the ion emitting surface; and

Have, for a given temperature, a vapor tension sufficient to obtain a quantity of ions necessary to neutralize essentially the space charge.

It so happens that the metals already known for their property of ease of ionization and already utilized for the compensation of the space charge in thermo-electronic converters, such as cesium, rubidium and potassium, also combine the totality of the preceding physical characteristics mentioned hereinabove, thereby permitting the same to be utilized as collectors with the advantages indicated hereinabove. In effect, the following table summarizes the characteristics thereof which are of interest in the application to thermo-electronic converters:

According to a preferred embodiment of the present invention, the collector will therefore be made of one of these metals, preferably of liquid cesium. The temperature of the collector during operation will be, for example, of the order of The materials of the other electrodes of the converter are suitably chosen, in such a manner that the specific weights and the working potential of the emitter are larger than the corresponding fiures of the table, and that the ionization potential of the collector is less than the working potential of the ion emitting surface, whereby this latter may coincide or not coincide with the emitter. Under these conditions, the metals such as tungsten, molybdenum, tantalum, columbium and rhenium are suitable for the emitter, but also non-homogeneous materials having a high emissive power may be utilized, provided they contain suflicient portions for the conditions indicated hereinabove. This is in particular the case for the cathodes with a supply or reservoir with a base of compressed and sintered powders of molybdenum and thorium, or with a base of barium carried by a refractory powder, etc.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate corresponding parts, and more particularly to FIG- URE 1, reference numeral 1 designates therein a metallic support for the emitter in which is embedded an emissive mass 2, for example, with a base of compressed and sintered powders of molybdenum and thorium. Reference numeral 3 designates in this figure a metallic support containing light metal 4 forming the collector in accordance with the present invention for example, made of cesium which becomes liquid at the operating temperature of the device.

The supports 1 and 3 are separated between themselves by an element 5 forming a vacuum-tight enclosure, this element 5, being, for example, made of insulating material but may also be made of any known resistive alloy such as nichrome or Kanthal. The operating temperature of the collector is chosen in such a manner that within the evacuated enclosure, there prevails a vapor pressure of cesium favorable to the obtaining of a suflicient quantity of ions to compensate for the space charge, this pressure being itself a function of the temperature of the emitter. For example, for an emitter of tungsten, this pressure may be of the order of 10- Torr, and the temperature of the collector may be of the order of 100 C. On the other hand, for an emitter with a base of compressed and sintered powders of molybdenum and thorium, this pressure is of the order of 1 Torr, and the temperature of the collector is then of the order of 300 C. This temperature will be maintained by heating means or cooling means of any suitable known construction, not illustrated in the drawing.

The converter is put into operation by causing the emitter 1 to be heated by a source of heat, preferably one of those which are normally lost such as sun rays, the heat of combustion or of the residual gases of engines, the losses in nuclear reactors, etc. The temperature of the emitter may be of the order of 900 to 1100 C. According to the physical mechanism referred to hereinabove, there is obtained between the conductors 7 and 8 connected respectively to the supports 1 and 3, an electrical utilizable voltage of which the positive pole is at 7 and the negative pole at 8. Reference numeral 6 illustrates in this figure the deposits of evaporated emissive material which, in accordance with the advantage obtained as a result of the present invention, no longer remain at the surface of the collector but fall to the bottom of the tank 3 and no longer disturb or endanger the proper operation of the converter.

By reason of the liquid state of the collector, the converter described herein can be utilized only in a predetermined position in which the surface of the emitter is parallel to the liquid surface of the collector which position establishes itself perpendicularly to the force of gravitation or acceleration. It is possible, within a certain measure and extent, to free the device according to the present invention from this shortcoming and to tolerate 'a certain inclination of the apparatus to the direction of the force of gravitation if the tank containing the liquid collector mass is subdivided into a suflicient number of compartments of which each offers a transverse section which is slight with respect to the total sur face of the collector. In the embodiment of FIGURE 2, in which the same reference numerals again designate the same elements as in FIGURE 1, these compartments are defined or limited by a certain number of annular partition Walls 9 disposed within the tank 3. The upper edge of these partition walls 9 extends above the liquid level 4 in such a manner that the liquid does not spill over from one compartment to the other when the tank 3 is inclined up to a certain limit whereas the entire surface remains, on the average, parallel to that of the emitter 2.

The modification of FIGURE 3, in which the same reference numerals again designate the same elements as FIGURES 1 and 2, differs from FIGURE 1 in that the bottom 10 of the tank 3 is inclined. Additionally, the device is completed by means of a forced circulatory system for the liquid metal, in accordance with known techniques described already in connection with collectors of liquid metal for high power tubes in the patent application Serial No. 92,217, filed on February 28, 1961 in the name of Gilbert Boucher and assigned to the assignee of the present application. This system comprises a closed-circuit pipe system 11 in which is inserted a suitable pump 12 of any known construction. A tank 13 for the deposit of impurities may also be provided in this closed circuit pipe system. As shown in FIGURE 3, the deposits of emissive material 6 are taken along by the circulation of the liquid 4, sliding along the inclined bottom 10 and are deposited at the bottom of the tank 13 outside the active space of the converter whereas the liquid 4 which is purified returns into that space.

In this manner, there is prevented soiling and/ or clogging of the tank over a long period of time.

While I have shown and described several embodi ments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of many changes and modifications within the spirit and scope thereof. For example, the present invention is not limited to diode converters, shown herein only for the sake of simplicity but is equally applicable, in the same manner, to triode converters, that is to those in which a special electrode, separate from the emitter and carried at the same or at a different potential is provided for the surface ionization. Additionally, the present invention is not limited to the particular materials described herein both as to the collector and emitter but encompasses all those converters of which the materials are chosen according to the general directives given hereinabove. Furthermore, the present invention is not limited to the structural embodiments shown herein but may be changed and modified in its actual structure Within the scope of a person skilled in the art.

Thus, it is obvious that the present invention is not limited to the specific details shown and described herein, but may be modified in numerous Ways within the scope of a person skilled in the art, and I, therefore, do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. An energy converter for directly converting thermal energy into electrical energy, comprising vacuum tight enclosure means, including means efiectively forming a tank with the bottom thereof inclined with respect to the horizontal in the normal operating position of said converter, emitter electrode means lodged within said tank and having a horizontally positioned surface insaid normal operating position and operative to emit electrons into said enclosure means upon application of heat to said emitter electrode means, collector electrode means with a surface portion thereof exposed to said enclosure means for collecting said electrons, said collector electrode means being made of a metal having a melting temperature that is lower than the normal operating temperature of said collector electrode means so as to become liquid at said operating temperature, said metal being selected from the group consisting of cesium, rubidium and potassium, and output means connected respectively to said emitter and collector electrode means to enable abstraction of the electrical energy appearing thereon upon application of heat energy to said emitter electrode means.

2. An energy converter for directly converting thermal energy into electrical energy, comprising vacuum tight enclosure means, emitter electrode means operative to emit electrons into said enclosure means upon application of heat to said emitter electrode means, collector electrode means disposed below said emitter electrode means and having a surface portion thereof exposed to said enclosure means for collecting said electrons, said collector electrode means being made of a metal having a melting temperature that is lower than the normal operating temperature of said collector electrode means so as to become liquid at said operating temperature and having a specific weight which is less than that of the emissive material so that any deposits that would normally form during operation on said collector surface portion move to the bottom of said liquid collector electrode means, means for removing the deposits emanating from said emitter electrode means from the bottom of said collector electrode means, and output means connected respectively to said emitter and collector electrode means to enable abstraction of the electrical energy appearing thereon upon application of heat energy to said emitter electrode means.

3. An energy converter for directly converting thermal energy into electrical energy, comprising vacuum tight enclosure means effectively constituting also metallic tank means, emitter electrode means accommodated within said tank means and operative to emit electrons into said enclosure means upon application of heat to said emitter electrode means, collector electrode means with a surface portion thereof exposed to said enclosure means for collecting said electrons, said collector electrode means being made of a metal having a melting temperature that is lower than the normal operating tempearture of said collector electrode means so as to become liquid at said operating temperature, output means connected respectively to said emitter and collector electrode means to enable abstraction of the electrical energy appearing thereon upon application of heat energy to said emitter electrode means, and means for effectively removing from said surface portion materials derived from said emitter means and deposited thereon during operation of the converter including second tank means, and connecting means operatively interconnecting said first and second tank means.

4. An energy converter for directly converting thermal energy into electrical energy, comprising vacuum tight enclosure means effectively constituting also metallic tank means, emitter electrode means accommodated within said tank means and operative to emit electrons into said enclosure means upon application of heat to said emitter electrode means, collector electrode means with a surface portion thereof exposed to said enclosure means for collecting said electrons, said collector electrode means being made of a metal having a melting temperature that is lower than the normal operating temperature of said collector electrode means so as to become liquid at said operating temperature, output means connected respectively to said emitter and collector electrode means to enable abstraction of the electrical energy appearing there- 7 a t 8 on upon application of heat energy to said emitter elec- References Cited by the Examiner trode means, and means for effectively removing from UNITED STATES PATENTS said surface portion materials derived from said emitter means and deposited thereon during operation of the con- 216371827 5/53 9 313-30 verter including a second tank means, connecting means 5 3,002,116 9/61 Flsher 3104 operatively interconnecting said first and second tank means into a closed circuit, and pump means in said con- MILTON HIRSHFIELD Primary Emmmer' necting means for circulating said liquid collector metal. DAVID X. SLINEY, Examiner. 

1. AN ENERGY CONVERTER FOR DIRECTLY CONVERTING THERMAL ENERGY INTO ELECTRICAL ENERGY, COMPRISING VACUUM TIGHT ENCLOSURE MEANS, INCLUDING MEANS EFFECTIVELY FORMING A TANK WITH THE BOTTOM THEREOF INCLINED WITH RESPECT TO THE HORIZONTAL IN THE NORMAL OPERATING POSITION OF SAID CONVERTER, EMITTER ELECTRODE MEANS LODGED WITHIN SAID TANK AND HAVING A HORIZONTALLY POSITIONED SURFACE IN SAID NORMAL OPERATING POOSITION AND OPERATIVE TO EMIT ELECTRONS INTO SAID ENCLOSURE MEANS UPON APPLICATION OF HEAT TO SAID EMITTER ELECTRODE MEANS, COLLECTOR ELECTRODE MEANS WITH A SURFACE PORTION THEREOF EXPOSED TO SAID ENCLOSURE MEANS FOR COLLECTING SAID ELECRONS, SAID COLLECTOR ELECTRODE MEANS BEING MADE OF A METAL HAVINGA MELTING TEMPERATURE THAT IS LOWER THAN THE NORMAL OPERATING TEMPERATURE OF SAID COLLECTOR ELECTRODE MEANS SO AS TO BECOME LIQUID AT SAID OPERATING TEMPERATURE, SAID METAL BEING SELECTED FROM THE GROUP CONSISTING OF CESIUM, RUBIDIUM AND POTASSIUM, AND OUTPUT MEANS CONNECTED RESPECTIVELY TO SAID EMITTER AND COLLECTOR ELECTRODE MEANS TO ENABLE ABSTRACTION OF THE ELECTRICAL ENERGY APPEARING THEREON UPON APPLICATION OF HEAT ENERGY TO SAID EMITTER ELECTRODE MEANS. 